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Claims  |
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What is claimed is:
1. A ceramic capacitor, comprising:
at least one dielectric ceramic layer consisting essentially of a
dielectric ceramic composition and at least two internal electrodes
sandwiching said dielectric ceramic composition;
said dielectric ceramic composition consisting essentially of a fired
mixture of a basic component of 100 parts by weight and an additional
component in the range of 0.2 to 5 parts by weight;
said basic component consisting essentially of a material represented by
the following formula:
{(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O}.sub.k (Ti.sub.1-y-z Zr.sub.y
R.sub.z)O.sub.2-z/2
where, R is one or more elements selected from the group consisting of Sc,
Y, Gd, Dy, Ho, Er, Yb, Tb, Tm and Lu; and w, x, y, z and k are numerals
fulfilling the following conditions:
0. 00.ltoreq.w.ltoreq.0.27
0.001.ltoreq.x.ltoreq.0.03
0.05.ltoreq.y.ltoreq.0.26
0.002.ltoreq.z.ltoreq.0.04
1.00.ltoreq.k.ltoreq.1.04
said additional component consisting essentially of Li.sub.2 O, SiO.sub.2
and MO wherein said MO is at least one oxide selected from the group
consisting of BaO, SrO, CaO, MgO and ZnO; and
a ratio among amounts of Li.sub.2 O, SiO.sub.2 and MO in said additional
component is within an area in a ternary system of mol % having five
vertexes of first to fifth vertexes wherein:
said first vertex A represents a condition in which amounts of Li.sub.2 O
is 1 mol %, SiO.sub.2 is 80 mol % and MO is 19 mol %;
said second vertex B represents a condition in which amounts of Li.sub.2 O
is 1 mol %, SiO.sub.2 is 39 mol % and MO is 60 mol %;
said third vertex C represents a condition in which amounts of Li.sub.2 O
is 30 mol %, SiO.sub.2 is 30 mol % and MO is 40 mol %;
said fourth vertex D represents a condition in which amounts of Li.sub.2 O
is 50 mol %, SiO.sub.2 is 50 mol % and MO is 0 mol %; and
said fifth vertex E represents a condition in which amounts of Li.sub.2 O
is 20 mol %, SiO.sub.2 is 80 mol % and MO is 0 mol %.
2. A ceramic capacitor, comprising:
at least one,dielectric ceramic layer consisting essentially of a
dielectric ceramic composition and at least two internal electrodes
sandwiching said dielectric ceramic composition;
said dielectric ceramic composition consisting essentially of a fired
mixture of a basic component of 100 parts by weight and an additional
component in the range of 0.2 to 5 parts by weight;
said basic component consisting essentially of a material represented by
the following formula:
{(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O}.sub.k (Ti.sub.1-y-z Zr.sub.y
R.sub.z)O.sub.2-z-2
where, R is one or more elements selected from the group consisting of Sc,
Y, Gd, Dy, Ho, Er, Yb, Tb, Tm and Lu; and w, x, y, z and k are numerals
fulfilling the following conditions:
0. 00.ltoreq.w.ltoreq.0.27
0.001.ltoreq.x.ltoreq.0.03
0.05.ltoreq.y.ltoreq.0.26
0.002.ltoreq.z.ltoreq.0.04
1.00.ltoreq.k.ltoreq.1.04
said additional component consisting essentially of B.sub.2 O.sub.3,
SiO.sub.2 and MO wherein said MO is at least one oxide selected from the
group consisting of BaO, SrO, CaO, MgO and ZnO; and
a ratio among amounts of B.sub.2 O.sub.3, SiO.sub.2 and MO in said
additional component is within an area in a ternary system diagram of mol
% having six vertexes of first to sixth vertexes, wherein:
said first vertex F represents a condition in which amounts of B.sub.2
O.sub.3 is 1 mol %, SiO.sub.2 is 80 mol % and MO is 19 mol %;
said second vertex G represents a condition in which amounts of B.sub.2
O.sub.3 is 1 mol %, SiO.sub.2 is 39 mol % and MO is 60 mol %;
said third vertex H represents a condition in which amounts of B.sub.2
O.sub.3 is 30 mol %, SiO.sub.2 is 0 mol % and MO is 70 mol %;
said fourth vertex I represents a condition in which amounts of B.sub.2
O.sub.3 is 90 mol %, SiO.sub.2 is 0 mol % and MO is 10 mol %;
said fifth vertex J represents a condition in which amounts of B.sub.2
O.sub.3 is 90 mol %, SiO.sub.2 is 10 mol % and MO is 0 mol %; and
said sixth vertex K represents a condition in which amounts of B.sub.2
O.sub.3 is 20 mol %, SiO.sub.2 is 80 mol % and MO is 0 mol %.
3. A ceramic capacitor, comprising:
at lease one dielectric ceramic layer consisting essentially of a
dielectric ceramic composition and at least two internal electrodes
sandwiching said dielectric ceramic composition;
said dielectric ceramic composition consisting essentially of a fired
mixture of a basic component of 100 parts by weight and an additional
component in the range of 0.2 to 5 parts by weight;
said basic component consisting essentially of a material represented by
the following formula:
{(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O}.sub.k (Ti.sub.1-y-z Zr.sub.y
R.sub.z)O.sub.2-z/2
where, R is one or more elements selected from the group consisting of Sc,
Y, Gd, Dy, Ho, Er, Yb, Tb, Tm and Lu; and w, x, y, z and k are numerals
fulfilling the following conditions:
0.00.ltoreq.w.ltoreq.0.27
0.001.ltoreq.x.ltoreq.0.03
0.05.ltoreq.y.ltoreq.0.26
0.002.ltoreq.z.ltoreq.0.04
1.00.ltoreq.k.ltoreq.1.04
said additional component consisting essentially of B.sub.2 O.sub.3,
SiO.sub.2 and Li.sub.2 O; and
a ratio among amounts of B.sub.2 O.sub.3, SiO.sub.2 and Li.sub.2 O in said
additional component is within an area in a ternary system diagram of mol
% having six vertexes of first to sixth vertexes wherein:
said first vertex L represents a condition in which amounts of B.sub.2
O.sub.3 is 1 mol %, SiO.sub.2 is 50 mol % and Li.sub.2 O is 49 mol %;
said second vertex M represents a condition in which amounts of B.sub.2
O.sub.3 is 50 mol %, SiO.sub.2 is 1 mol % and Li.sub.2 O is 49 mol %;
said third vertex N represents a condition in which amounts of B.sub.2
O.sub.3 is 80 mol %, SiO.sub.2 is 1 mol % and Li.sub.2 O is 19 mol %;
said fourth vertex O represents a condition in which amounts of B.sub.2
O.sub.3 is 89 mol %, SiO.sub.2 is 10 mol % and Li.sub.2 O is 1 mol %;
said fifth vertex P represents a condition in which amounts of B.sub.2
O.sub.3 is 19 mol %, SiO.sub.2 is 80 mol % and Li.sub.2 O is 1 mol %; and
said sixth vertex Q represents a condition in which amounts of B.sub.2
O.sub.3 is 1 mol %, SiO.sub.2 is 80 mol % and Li.sub.2 O is 19 mol %.
4. A method for fabricating a ceramic capacitor, comprising the steps of:
providing a mixture of non-sintered ceramic powder;
forming a non-sintered ceramic sheet consisting of said mixture;
fabricating a laminated structure in which said non-sintered ceramic sheet
is sandwiched between at least two conductive paste layers;
firing said laminated structure under a non-oxidative atmosphere; and
heating said fired laminated structure under an oxidative atmosphere;
said mixture of non-sintered ceramic powder consisting essentially of a
fired mixture of a basic component of 100 parts by weight and an
additional component in the range of 0.2 to 5 parts by weight;
said basic component consisting essentially of a material represented by
the following formula:
{(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O}.sub.k (Ti.sub.1-y-z Zr.sub.y
R.sub.z)O.sub.2-z/2
where, R is one or more elements selected from the group consisting of Sc,
Y, Gd, Dy, Ho, Er, Yb, Tb, Tm and Lu; and w, x, y, z and k are numerals
fulfilling the following conditions:
0. 00.ltoreq.w.ltoreq.0.27
0.001.ltoreq.x.ltoreq.0.03
0.05.ltoreq.y.ltoreq.0.26
0.002.ltoreq.z.ltoreq.0.04
1.00.ltoreq.k.ltoreq.1.04
said additional component consisting essentially of Li.sub.2 O, SiO.sub.2
and MO wherein said MO is at least one oxide selected from the group
consisting of BaO, SrO, CaO, MgO and ZnO; and
a ratio among amounts of Li.sub.2 O, SiO.sub.2 and MO in said additional
component is within an area in a ternary system diagram of mol % having
five vertexes of first to fifth vertexes, wherein:
said first vertex A represents a condition in which amounts of Li.sub.2 O
is 1 mol %, SiO.sub.2 is 80 mol % and MO is 19 mol %;
said second vertex B represents a condition in which amounts of Li.sub.2 O
is 1 mol %, SiO.sub.2 is 39 mol % and MO is 60 mol %;
said third vertex C represents a condition in which amounts of Li.sub.2 O
is 30 mol %, SiO.sub.2 is 30 mol % and MO is 40 mol %;
said fourth vertex D represents a condition in which amounts of Li.sub.2 O
is 50 mol %, SiO.sub.2 is 50 mol % and MO is 0 mol %; and
said fifth vertex E represents a condition in which amounts of Li.sub.2 O
is 20 mol %, SiO.sub.2 is 80 mol % and MO is 0 mol %.
5. A method for fabricating a ceramic capacitor, comprising the steps of:
providing a mixture of non-sintered ceramic powder;
forming a non-sintered ceramic sheet consisting of said mixture;
fabricating a laminated structure in which said non-sintered ceramic sheet
is sandwiched between at least two conductive paste layers;
firing said laminated structure under a non-oxidative atmosphere; and
heating said fired laminated structure under an oxidative atmosphere;
said mixture of non-sintered ceramic powder consisting essentially of a
fired mixture of a basic component of 100 parts by weight and an
additional component in the range of 0.2 to 5 parts by weight;
said basic component consisting essentially of a material represented by
the following formula:
{(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O}.sub.k (Ti.sub.1-y-z Zr.sub.y
R.sub.z)O.sub.2-z/2
where, R is one or more metal elements selected from the group consisting
of Sc, Y, Gd, Dy, Ho, Er, Yb, Tb, Tm and Lu; and w, x, y, z and k are
numerals fulfilling the following conditions:
0. 00.ltoreq.w.ltoreq.0.27
0.001.ltoreq.x.ltoreq.0.03
0.05.ltoreq.y.ltoreq.0.26
0.002.ltoreq.z.ltoreq.0.04
1.00.ltoreq.k.ltoreq.1.04
said additional component consisting essentially of B.sub.2 O.sub.3,
SiO.sub.2 and MO wherein said MO is at least one oxide selected from the
group consisting of BaO, SrO, CaO, MgO and ZnO; and
a ratio among amounts of B.sub.2 O.sub.3, SiO.sub.2 and MO in said
additional component is within an area in a ternary system diagram of mol
% having six vertexes of first to sixth vertexes wherein:
said first vertex F represents a condition in which amounts of B.sub.2
O.sub.3 is 1 mol %, SiO.sub.2 is 80 mol % and MO is 19 mol %;
said second vertex G represents a condition in which amounts of B.sub.2
O.sub.3 is 1 mol %, SiO.sub.2 is 39 mol % and MO is 60 mol %;
said third vertex H represents a condition in which amounts of B.sub.2
O.sub.3 is 30 mol %, SiO.sub.2 is 0 mol % and Li.sub.2 O is 70 mol %;
said fourth vertex I represents a condition in which amounts of B.sub.2
O.sub.3 is 90 mol %, SiO.sub.2 is 0 mol % and MO is 10 mol %;
said fifth vertex J represents a condition in which amounts of B.sub.2
O.sub.3 is 90 mol %, SiO.sub.2 is 10 mol % and MO is 0 mol %; and
said sixth vertex K represents a condition in which amounts of B.sub.2
O.sub.3 is 20 mol %, SiO.sub.2 is 80 mol % and MO is 0 mol %.
6. A method for fabricating a ceramic capacitor, comprising the steps of:
providing a mixture of non-sintered ceramic powder;
forming a non-sintered ceramic sheet consisting of said mixture;
fabricating a laminated structure in which said non-sintered ceramic sheet
is sandwiched between at least two conductive paste layers;
firing said laminated structure under a non-oxidative atmosphere; and
heating said fired laminated structure under an oxidative atmosphere;
said mixture of non-sintered ceramic powder consisting essentially of a
fired mixture of a basic component of 100 parts by weight and an
additional component in the range of 0.2 to 5 parts by weight;
said basic component consisting essentially of a material represented by
the following formula:
{(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O}.sub.k (Ti.sub.1-y-z Zr.sub.y
R.sub.z)O.sub.2-z/2
where, R is one or more metal elements selected from the group consisting
of Sc, i y, Gd, Dy, Ho, Er, Yb, Tb, Tm and Lu; and w, x, y, z and k are
numerals fulfilling the following conditions:
0.00.ltoreq.w.ltoreq.0.27
0.001.ltoreq.x.ltoreq.0.03
0.05.ltoreq.y.ltoreq.0.26
0.002.ltoreq.z.ltoreq.0.04
1.00.ltoreq.k.ltoreq.1.04
said additional component consisting essentially of B.sub.2 O.sub.3,
SiO.sub.2 and Li.sub.2 O; and
a ratio among amounts of B.sub.2 O.sub.3, SiO.sub.2 and Li.sub.2 O in said
additional component is within an area in a ternary system diagram of mol
% having six vertexes of first to sixth vertexes wherein:
said first vertex L represents a condition in which amounts of B.sub.2
O.sub.3 is 1 mol %, SiO.sub.2 is 50 mol % and Li.sub.2 O is 49 mol %;
said second vertex M represents a condition in which amounts of B.sub.2
O.sub.3 is 50 mol %, SiO.sub.2 is 1 mol % and Li.sub.2 O is 49 mol %;
said third vertex N represents a condition in which amounts of B.sub.2
O.sub.3 is 80 mol %, SiO.sub.2 is 1 mol % and Li.sub.2 O is 19 mol %;
said fourth vertex O represents a condition in which amounts of B.sub.2
O.sub.3 is 89 mol %, SiO.sub.2 is 10 mol % and Li.sub.2 O is 1 mol %;
said fifth vertex P represents a condition in which amounts of B.sub.2
O.sub.3 is 19 mol %, SiO.sub.2 is 80 mol % and Li.sub.2 O is 1 mol %; and
said sixth vertex Q represents a condition in which amounts of B.sub.2
O.sub.3 is 1 mol %, SiO.sub.2 is 80 mol % and Li.sub.2 O is 19 mol %. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a ceramic capacitor having a one-layer structure
or a laminated structure in which one or more than one dielectric ceramic
layer is (are) sandwiched between two or more internal electrodes, and a
method for fabricating the same.
2. Description Of Related Art
In a conventional method for fabricating a laminated ceramic capacitor, a
desired pattern of conductive paste consisting mainly of noble metal such
as platinum or palladium is printed on a non-sintered ceramic sheet (a
green sheet) consisting essentially of dielectric ceramic material powder.
Then, a plural number of the green sheets are laminated, pressed and
attached to each other, and the laminated green sheets are fired at a
temperature in the range of 1300.degree. C. to 1600.degree. C. under an
oxidative atmosphere. The non-sintered ceramic sheets become dielectric
ceramic layers by the firing and the conductive paste becomes an internal
electrode by the firing.
As described above, by adopting the conductive paste consisting mainly of
noble metal such as platinum or palladium, a desired conductive internal
electrode can be obtained without oxidation thereof even if the material
thereof is fired at a high temperature in the range of 1300.degree. C. to
1600.degree. C. under an oxidative atmosphere.
However, noble metals such as platinum or palladium are expensive, so that
the laminated ceramic capacitor become very costly.
In order to resolve the problem described above, the applicants of the
present invention have proposed several solutions in Japanese Patent
Publication No. 20851/85, Japanese Patent Provisional Publication No.
147404/86, Japanese Patent Provisional Publication No. 147405/86, and
Japanese Patent Provisional Publication No. 147406/86.
Japanese Patent Publication No. 20851/85 discloses dielectric ceramic
compositions including basic components consisting essentially of
{(Ba.sub.x Ca.sub.y Sr.sub.z)O}.sub.k (Ti.sub.n Zr.sub.1-n)O.sub.2
and additional components consisting essentially of Li.sub.2 O, SiO.sub.2
and MO (MO is one or more than one kind of oxide selected from the group
consisting of BaO, CaO and SrO).
Japanese Patent Provisional Publication No. 147404/86 discloses dielectric
ceramic compositions including basic components consisting essentially of
{(Ba.sub.1-x-y Ca.sub.x Sr.sub.y)}.sub.k (Ti.sub.1-z Zr.sub.z)O.sub.2
and additional components consisting essentially of B.sub.2 O.sub.3,
SiO.sub.2 and Li.sub.2 O.
Japanese Patent Provisional Publication No. 147405/86 discloses dielectric
ceramic compositions including basic components consisting essentially of
{(Ba.sub.1-x-y Ca.sub.x Sr.sub.y)O}.sub.k (Ti.sub.1-z Zr.sub.z)O.sub.2
and additional components consisting essentially of B.sub.2 O.sub.3 and
SiO.sub.2.
Japanese Patent Provisional Publication No. 147406/86 discloses dielectric
ceramic compositions including basic components consisting essentially of
{(Ba.sub.1-x-y Ca.sub.x Sr.sub.y)O}.sub.k (Ti.sub.1-z Zr.sub.z)O.sub.2
and additional components consisting essentially of B.sub.2 O.sub.3,
SiO.sub.2 and MO (MO is one or more than one kind of oxide selected from
the group consisting essentially of BaO, CaO and SrO).
The dielectric ceramic compositions disclosed in these Publications have a
dielectric constant .epsilon..sub.s of at least 5000, and a resistivity
.rho. of at least 1.times.10.sup.6 M.OMEGA..multidot.cm. By using one of
the above dielectric ceramic compositions as a dielectric layer and a
conductive paste consisting mainly of base metal such as nickel (Ni) as
internal electrodes and firing same at a temperature of up to 1200.degree.
C. under a reductive (non-oxidative atmosphere), ceramic capacitors with
improved electric characteristics can be obtained at a low cost.
Recently, electric circuits have become highly dense. These circuits
require miniaturization of ceramic capacitors, especially those having a
laminated structure. It has been desired to make the dielectric constant
.epsilon..sub.s of the dielectric ceramic compositions still larger,
without degrading the other electric characteristics below those of the
dielectric ceramic compositions disclosed in the above cited references.
SUMMARY OF THE INVENTION
An improved ceramic capacitor is provided with a dielectric ceramic
composition having a dielectric constant .epsilon..sub.s of at least 7000,
a dielectric loss (tan .delta.) of up to 2.5%, and a resistivity .rho. of
at least 1.times.10.sup.6 M.OMEGA..multidot.cm, by firing the composition
up to 1200.degree. C. in a non-oxidative atmosphere. The dielectric
ceramic composition consists essentially of a fired mixture of a basic
component of 100 parts by weight and 0.2 to 5 parts by weight of an
additional component. The basic component consisting essentially of a
material represented by the following formula:
{(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O}.sub.k (Ti.sub.1-y-z Zr.sub.y
R.sub.z)O.sub.2-z/2
where, R is one or more elements selected from the group consisting of Sc,
Y, Gd, Dy, Ho, Er, Yb, Tb, Tm and Lu; and w, x, y, z and k are numerals
fulfilling the following conditions:
0.00.ltoreq.w.ltoreq.0.27
0.001.ltoreq.x.ltoreq.0.03
0.05.ltoreq.y.ltoreq.0.26
0.002.ltoreq.z.ltoreq.0.04
1.00.ltoreq.k.ltoreq.1.04
The additional component consists essentially of Li.sub.2 O, SiO.sub.2 and
MO, wherein said MO is at least one oxide selected from the group
consisting of BaO, SrO, CaO, MgO and ZnO.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view illustrating an example of a laminated
ceramic capacitor according to the present invention;
FIG. 2 is a ternary-system diagram showing the composition ratio of the
additional component according to the first and fourth preferred
embodiments herein;
FIG. 3 is a ternary-system diagram showing the composition ratio of the
additional component according to the second and fifth preferred
embodiments herein; and
FIG. 4 is a ternary-system diagram showing the composition ratio of the
additional component according to the third and sixth preferred
embodiments herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to a first preferred embodiment, the ceramic capacitor includes
at least one dielectric ceramic layer consisting essentially of a
dielectric ceramic composition and at least two internal electrodes in the
dielectric ceramic composition.
The dielectric ceramic composition consists essentially of a fired mixture
of a basic component of 100.0 parts by weight and an additional component
in the range of 0.2 to 5.0 parts by weight.
The basic component consisting essentially of a material represented by the
following formula:
{(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O}.sub.k (Ti.sub.1-y-z Zr.sub.y
R.sub.z)O.sub.2-z/2
where, R is one or more elements selected from the group consisting of Sc,
Y, Gd, Dy, Ho, Er, Yb, Tb, Tm and Lu, and, w, x, y, z and k are numerals
fulfilling the following conditions:
0.00.ltoreq.w.ltoreq.0.27
0.001.ltoreq.x.ltoreq.0.03
0.05.ltoreq.y.ltoreq.0.26
0.002.ltoreq.z.ltoreq.0.04
1.00.ltoreq.k.ltoreq.1.04
The an additional component consists essentially of Li.sub.2 O, SiO.sub.2
and MO (MO is at least one oxide selected from the group consisting of
BaO, SrO, CaO, MgO and ZnO).
The range of the ratio of the amounts of Li.sub.2 O, SiO.sub.2 and MO in
the additional component is represented by an area having five vertexes in
the ternary system diagram of mol % as follows:
the first vertex A where the amount of Li.sub.2 O is 1 mol %, SiO.sub.2 is
80 mol % and MO is 19 mol %;
the second vertex B where the amount of Li.sub.2 O is 1 mol %, SiO.sub.2 is
39 mol % and MO is 60 mol %;
the third vertex C where the amount of Li.sub.2 O is 30 mol %, SiO.sub.2 is
30 mol % and MO is 40 mol %;
the fourth vertex D where the amount of Li.sub.2 O is 50 mol %, SiO.sub.2
is 50 mol % and MO is 0 mol %; and
the fifth vertex E where the amount of Li.sub.2 O is 20 mol %, SiO.sub.2 is
80 mol % and MO is 0 mol %.
A dielectric ceramic composition having the desired electric
characteristics, i.e. a high dielectric constant .epsilon..sub.s, and a
high resistivity .rho. can be obtained on the condition of
0.00.ltoreq.w.ltoreq.0.27 (w represents the ratio of Ca in the composition
formula of the basic component). However, if w is larger that 0.27 the
firing temperature will be high (up to 1250.degree. C.), and the
dielectric constant .epsilon..sub.s will be smaller than 7000.
Ca is added mainly to make the temperature characteristics of the ceramic
capacitor flat and to improve the resistivity .rho.. However, sintered
materials having desired electric characteristics can be obtained without
the addition of Ca. In such cases the lower limit of w is 0.00.
A dielectric ceramic composition having the desired electric
characteristics can be obtained on the condition of
0.001.ltoreq.x.ltoreq.0.03 (x represents the ratio of Mg in the
composition formula of the basic component). However, the dielectric
constant .epsilon..sub.s drops to less than 7000, if x is larger than
0.03.
Mg can shift the Curie point to a lower temperature, make the temperature
characteristics flat, and improve the resistivity .rho.. There is observed
a significant effect if x is smaller than 0.03, even in the vicinity of 0.
However, it is desirable that x is at least 0.001 since the electric
characteristics should not vary with mass produced capacitors.
A dielectric ceramic composition having desired electric characteristics
can be obtained on the condition of 0.05.ltoreq.y.ltoreq.0.26 (y
represents the ratio of Zr in the composition formula of the basic
component). However, the dielectric constant .epsilon..sub.s is smaller
than 7000, if y is smaller than 0.05 or larger than 0.26.
A dielectric ceramic composition having desired electric characteristics
can be obtained on the condition of 0.002.ltoreq.z.ltoreq.0.04 (z
represents the ratio of R in the composition formula of the basic
component). However, the dielectric loss (tan .delta.) becomes
considerable and the resistivity .rho. is smaller than 1.times.10.sup.4
M.OMEGA..multidot.cm, if z is smaller than 0.002. On the other hand, if z
is larger than 0.04, a dense sintered material cannot be obtained, even if
the firing temperature is 1250.degree. C.
The R component Sc, Y, Gd, Dy, Ho, Er, Yb, Tb, Tm, and Lu perform almost
the same function, so that any one or more of them can be used. Tb, Tm,
and Lu are not involved in Table 3 shown hereinafter, but they have the
same effect as the other R components.
A dielectric ceramic composition having desired electric characteristics
can be obtained on the condition of 1.00.ltoreq.k.ltoreq.1.04 (k
represents the ratio of {(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O} in the
composition formula of the basic component). However, the resistivity
.rho. becomes smaller than 1.times.10.sup.6 M.OMEGA..multidot.cm and tan
.delta. becomes large, if k is smaller than 1.00. On the other hand, a
dense sintered material cannot be obtained, even if the firing temperature
is 1250.degree. C., if k is larger than 1.04.
A small amount (desirably in the range of 0.05 to 0.01 weight %) of
mineralizers such as MnO.sub.2 may be added to the basic component to
improve the sintering characteristic thereof so long as the materializers
do not interfere with the electric characteristics of the capacitor. Other
materials may be also added if necessary. The starting materials for the
basic component may include oxides, hydroxides or other compounds, in
addition to the compounds described in the preferred embodiments herein.
If the amount of the additional component is in the range of 0.2 to 5.0
parts by weight in 100 parts by weight of the basic component, a sintered
material having desired electric characteristics can be obtained by firing
at a temperature in the range of 1190.degree. C. to 1200.degree. C.
However, a dense sintered material cannot be obtained, even if the firing
temperature is 1250.degree. C., if the amount of the additional component
is smaller than 0.2 parts by weight. On the other hand, the dielectric
constant .epsilon..sub.s becomes smaller than 7000, if the amount of the
additional component is larger than 5.0 parts by weight.
A sintered material having desired electric characteristics can be obtained
if the ratio between the amounts of Li.sub.2 O, SiO.sub.2 and MO in the
additional component is within the area in the ternary system diagram of
mol % described above. However, a dense sintered material cannot be
obtained, if the ratio of these components is out of the circumscribed
area. The MO component may be one or more metal oxides selected from the
group consisting of BaO, SrO, CaO, MgO and ZnO, in the proper ratio.
The second preferred embodiment is a ceramic capacitor having at least one
dielectric ceramic layer consisting essentially of a dielectric ceramic
composition and at least two internal electrodes in the dielectric ceramic
composition.
The dielectric ceramic composition consists essentially of a fired mixture
of a basic component of 100.0 parts by weight and an additional component
in the range of 0.2 to 5.0 parts by weight.
The basic component consists essentially of a material represented by the
following formula:
{(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O}.sub.k (Ti.sub.1-y-z Zr.sub.y
R.sub.z)O.sub.2-z/2
where, R is one or more elements selected from the group consisting of Sc,
Y, Gd, Dy, Ho, Er, Yb, Tb, Tm and Lu, and, w, x, y, z and k are numerals
fulfilling the following conditions:
0.00.ltoreq.w.ltoreq.0.27
0.001.ltoreq.x.ltoreq.0.03
0.05.ltoreq.y.ltoreq.0.26
0.002.ltoreq.z.ltoreq.0.04
1.00.ltoreq.k.ltoreq.1.04
The additional component consists essentially of B.sub.2 O.sub.3, SiO.sub.2
and MO (MO is at least one oxide selected from the group consisting of
BaO, SrO, CaO, MgO and ZnO.
The range in the ratio of the amounts of B.sub.2 O.sub.3, SiO.sub.2 and MO
in the additional component is represented by an area having six vertexes
in the ternary system diagram of mol %, as follows:
the first vertex F where the amount of B.sub.2 O.sub.3 is 1 mol %,
SiO.sub.2 is 80 mol % and MO is 19 mol %;
the second vertex G where the amount of B.sub.2 O.sub.3 is 1 mol %,
SiO.sub.2 is 39 mol % and MO is 60 mol %;
the third vertex H where the amount of B.sub.2 O.sub.3 is 30 mol %,
SiO.sub.2 is 0 mol % and MO is 70 mol %;
the fourth vertex I where the amount of B.sub.2 O.sub.3 is 90 mol %,
SiO.sub.2 is 0 mol % and MO is 10 mol %;
the fifth vertex J where the amount of B.sub.2 O.sub.3 is 90 mol %,
SiO.sub.2 is 10 mol % and MO is 0 mol %; and
the sixth vertex K where the amount of B.sub.2 O.sub.3 is 20 mol %,
SiO.sub.2 is 80 mol % and MO is 0 mol %.
In the second preferred embodiment, the content of both the basic component
and the additional component are the same as in the first preferred
embodiment. A sintered material having desired electric characteristics
can be obtained if the ratio of the amounts of B.sub.2 O.sub.3, SiO.sub.2
and MO in the additional component is within the area in the ternary
system diagram of mol % described above. However, a dense sintered
material cannot be obtained, if the ratio of the additional component is
out of the above described range. The MO component may be one or more of
the metal oxides selected from the group consisting of BaO, SrO, CaO, MgO
and ZnO, in the proper amount.
The third preferred embodiment, the ceramic capacitor, includes at least
one dielectric ceramic layer consisting essentially of a dielectric
ceramic composition and at least two internal electrodes in the dielectric
ceramic composition.
The dielectric ceramic composition consists essentially of a fired mixture
of a basic component of 100.0 parts by weight and an additional component
in the range of 0.2 to 5.0 parts by weight.
The basic component consists essentially of a material represented by the
following formula:
{(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O}.sub.k (Ti.sub.1-y-z Zr.sub.y
R.sub.z)O.sub.2-z/2
where, R is one or more elements selected from the group consisting of Sc,
Y, Gd, Dy, Ho, Er, Yb, Tb, TIn and Lu, and w, x, y, z and k are numerals
fulfilling the following conditions:
0.00.ltoreq.w.ltoreq.0.27
0.001.ltoreq.x.ltoreq.0.03
0.05.ltoreq.y.ltoreq.0.26
0.002.ltoreq.z.ltoreq.0.04
1.00.ltoreq.k.ltoreq.1.04
The additional component consists essentially of B.sub.2 O.sub.3, SiO.sub.2
and Li.sub.2 O.
The range of the ratio of the amounts of B.sub.2 O.sub.3, SiO.sub.2 and
Li.sub.2 O in the additional component is represented by an area having
six vertexes in the ternary system diagram of mol %, as follows:
the first vertex L where the amount of B.sub.2 O.sub.3 is 1 mol %,
SiO.sub.2 is 50 mol % and Li.sub.2 O is 49 mol %;
the second vertex M where the amount of B.sub.2 O.sub.3 is 50 mol %,
SiO.sub.2 is 1 mol % and Li.sub.2 O is 49 mol %;
the third vertex N where the amount of B.sub.2 O.sub.3 is 80 mol %,
SiO.sub.2 is 1 mol % and Li.sub.2 O is 19 mol %;
the fourth vertex O where the amount of B.sub.2 O.sub.3 is 89 mol %,
SiO.sub.2 is 10 mol % and Li.sub.2 O is 1 mol %;
the fifth vertex P where the amount of B.sub.2 O.sub.3 is 19 mol %,
SiO.sub.2 is 80 mol % and Li.sub.2 O is 1 mol %; and
the sixth vertex Q where the amount of B.sub.2 O.sub.3 is 1 mol %,
SiO.sub.2 is 80 mol % and Li.sub.2 O is 19 mol %.
The content of both the basic component and the additional component are
the same as in the first preferred embodiment. A sintered material having
desired electric characteristics can be obtained if the ratio of the
amounts of B.sub.2 O.sub.3, SiO.sub.2 and Li.sub.2 O in the additional
component is within the area in the ternary system diagram of mol %
described above. However, a dense sintered material cannot be obtained if
the ratio is outside of this area.
In a fourth preferred embodiment a method is provided for fabricating a
ceramic capacitor which includes the steps of providing a mixture of
non-sintered ceramic powder consisting essentially of basic and additional
components as in the first preferred embodiment herein, forming a
non-sintered ceramic sheet consisting of the mixture, fabricating a
laminated structure in which the non-sintered ceramic sheet is sandwiched
between at least two conductive paste layers, firing the laminated
structure under a non-oxidative atmosphere, and heating the fired
laminated structure under an oxidative atmosphere.
In a fifth preferred embodiment, a method is provided for fabricating a
ceramic capacitor which includes the steps of providing a mixture of
non-sintered ceramic powder consisting essentially of basic and additional
components as in the second preferred embodiment herein, forming a
non-sintered ceramic sheet consisting of the mixture, fabricating a
laminated structure in which the non-sintered ceramic sheet is sandwiched
between at least two conductive paste layers, firing the laminated
structure under a non-oxidative atmosphere, and heating the fired
laminated structure under an oxidative atmosphere.
In a sixth preferred embodiment, a method is provided for fabricating a
ceramic capacitor which includes the steps of providing a mixture of
non-sintered ceramic powder consisting essentially of basic and additional
components as in the third embodiment herein, forming a non-sintered
ceramic sheet consisting of the mixture, fabricating a laminated structure
in which the non-sintered ceramic sheet is sandwiched between at least two
conductive paste layers, firing the laminated structure under a
non-oxidative atmosphere, and heating the fired laminated structure under
an oxidative atmosphere.
In the fourth to sixth preferred embodiments herein, the non-oxidative
atmosphere may be a neutral atmosphere such as in N.sub.2 or Ar, in
addition to a reductive atmosphere such as in H.sub.2 or CO. The
temperature in the firing under a non-oxidative atmosphere can be changed
depending on electrode materials used. If Ni is adopted as the material of
the inner electrode, cohesion of Ni particles may be insufficient at
temperatures in the range of 1050.degree. C. to 1200.degree. C.
The temperature at which the fired laminated structure is heated under an
oxidative atmosphere should be lower than the temperature of the firing
under a non-oxidative atmosphere, the preferred temperature being in the
range of 500.degree. C. to 1000.degree. C. The oxidative atmosphere is not
limited to air. A low oxygen atmosphere, for example, can be used where
some ppm of O.sub.2 are mixed in N.sub.2, or an atmosphere with any oxygen
partial pressure can be used. The temperature and the oxygen partial
pressure must be changed in consideration of oxidation of the electrode
materials such as Ni and the dielectric ceramic materials. Although the
temperature of heating the fired laminated structure is 600.degree. C. in
the embodiments as described hereinafter, other heating temperatures can
be used.
In the preferred embodiments, the heating under a non-oxidative atmosphere
and the heating under an oxidative atmosphere are described as being
performed in a series of heating steps. However, it is possible that the
heating steps can be performed in two different processes.
In the preferred embodiments, Zn is used as the external electrode, but Ni,
Ag, and Cu are also available depending on the plating condition of the
electrode. Firing of the laminated structure and plating the external
electrode can be carried out at the same time by coating the surface of
the non-sintered laminated structure with an external electrode of Ni.
Although ceramic capacitors having laminated structures are described
herein, the present inventions may be applied generally to ceramic
capacitors such as those having a one-layer structure.
Example 1:
Dielectric ceramic compositions in the first and fourth preferred
embodiments were prepared.
The composition of Sample No. 1 is shown in Table 3-1.
MAKING THE BASIC COMPONENT
Compounds in Table 1 are weighed, poured into a pot mill with alumina balls
and 2.5 l of water, stirred and mixed for 15 hours to obtain a material
mixture.
TABLE 1
______________________________________
compounds weight (g)
mol portion
______________________________________
BaCO.sub.3 657.81 93.425
CaCO.sub.3 25.25 7.07
MgO 0.73 0.505
TiO.sub.2 236.62 83.0
ZrO.sub.2 65.95 15.0
Er.sub.2 O.sub.3
13.65 1.0
______________________________________
The values of the weight (g) of the compounds in Table 1 are calculated so
that the composition formula of the basic component:
{(Ba.sub.1-w-x Ca.sub.w Mg.sub.x)O}.sub.k (Ti.sub.1-y-z Zr.sub.y
R.sub.z)O.sub.2-z/2
becomes:
{(Ba.sub.0.925 Ca.sub.0.07 Mg.sub.0.005)O}.sub.1.01 (Ti.sub.0.83
Zr.sub.0.15 Er.sub.0.02)O.sub.1.99 (1)
Next, the material mixture is poured into a stainless pot and dried for 4
hours at 150.degree. C. using a hot blast drier. The dried material
mixture is roughly ground and then baked for 2 hours at 1200.degree. C. in
air using a tunnel furnace. The powder of the basic component in the
composition formula (1) is obtained.
MAKING THE ADDITIONAL COMPONENT
The compounds in Table 2 are weighed, mixed with 300 cc of alcohol, and
stirred for 10 hours in a polyethylene pot using aluminum balls to obtain
the desired mixture.
TABLE 2
______________________________________
compounds weight (g)
mol portion
______________________________________
Li.sub.2 O 0.44 1
SiO.sub.2 70.99 80
BaCO.sub.3 11.10 3.8
CaCO.sub.3 14.70 9.5
MgO 3.40 5.7
______________________________________
The values of the weight (g) of the compounds in Table 2 are calculated so
that the Li.sub.2 O is 1 mol %, SiO.sub.2 is 80% mol %, and MO is 19 mol %
{BaO (3.8 mol %)+CaO (9.5 mol %)+MgO (5.7 mol %)}. The proportions of BaO,
CaO and MgO in MO is 20 mol %, 50 mol % and 30 mol %, respectively.
The mixture is baked for two hours at 1000.degree. C. in air and then
poured into an alumina pot with 300 cc of water and ground for 15 hours
using alumina balls. The ground mixture is dried for 4 hours at
150.degree. C., and a powder of the additional component is obtained.
MAKING SLURRY
2 parts by weight (20 g) of the additional component is added to 100 parts
by weight (1000 g) of the basic component. Then, the mixture of the basic
and additional components are mixed with 15 weight % of organic binder
consisting of an aqueous solution of acryl acid ester polymer, glycerin
and condensed phosphate and 50 weight % of water. The resulting mixture
is poured into a ball mill, ground and mixed to obtain a slurry of a
dielectric ceramic material.
MAKING NON-SINTERED CERAMIC SHEET
The slurry is poured into a vacuum foam remover and the foam is removed
therefrom. The defoamed slurry is then poured into a reverse roll coater
to form a molded thin sheet which is continuously laid on a long polyester
film. The molded thin sheet is heated to 100.degree. C. on the polyester
film until it is dry, and a non-sintered ceramic sheet having a thickness
of approximately 25 .mu.m is obtained. The non-sintered ceramic sheet
having a large length is cut into 10 cm square segme | | |
